Method of controlling air-fuel ratio and ignition timing in internal combustion engine and apparatus therefor

ABSTRACT

In a steady running condition of a vehicle, an air-fuel ratio is controlled to be equalized in value to a target air-fuel lener than a stoichiometric air-fuel ratio and an ignition timing is controlled to be equalized in value to a required ignition timing, so that a fuel consumption can be improved.

This is a division of application Ser. No. 590,053 filed Mar. 15, 1984,now U.S. Pat. No. 4,559,915.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and an apparatus for controlling anair-fuel ratio and an ignition timing in an internal combustion engine,and more particularly to a method of and the apparatus for controllingan air-fuel ratio and an ignition timing in a steady running conditionof spark-ignition engine.

2. Description of the Prior Art

In the spark-ignition engines in general, there has been used athree-way catalytic converter for purifying carbon monoxide, hydrocarbonand nitric oxide in the exhaust gas. To improve the rate of purificationof this three-way catalytic converter, a fuel injection valve or a fuelinjection nozzle is on-off controlled by a basic fuel injectionpulse-width based on an engine rotational speed and an engine load (anintake pipe pressure or an intake air flowrate per turn of the engine),so that an air-fuel ratio of an air-fuel mixture can be controlled to bein the vicinity of a stoichiometric air-fuel ratio. Since a requiredignition timing of the engine is varied depending upon the enginerotational speed and the engine load, the ignition timing is controlledso that the required ignition timing can be obtained depending upon theengine rotational speed and engine load.

In consequence, during the normal running condition excluding the caseof a high load, the air-fuel ratio is controlled to be in the vicinityof the stoichiometric air-fuel ratio irrespective of an acceleration, aconstant speed and a deceleration, and hence, the air-fuel ratio is notcontrolled to be one where the best fuel consumption rate can beattained in the conditions of running at a substantially constant speed.

SUMMARY OF THE INVENTION

The present invention has as its object the provision of method of andapparatus for controlling an air-fuel ratio and an ignition timing in aninternal combustion engine, in which the air-fuel ratio is made leanerand the ignition timing is corrected to improve the fuel consumptionduring steady running condition.

To this end, the arrangement according to a first aspect of the presentinvention comprises; a first step of judging whether or not a vehicle isin a steady running condition; a second step of gradually controllingthe air-fuel ratio every predetermined period of time so that theair-fuel ratio can coincide with a target air-fuel ratio, which has beenpredetermined to a value leaner than the stoichiometric air-fuel ratio,in accordance with an engine operating condition, when it is judged thatthe vehicle is in the steady running condition; and a third step ofgradually controlling the ignition timing every predetermined period oftime so that the ignition timing can coincide with a required ignitiontiming corresponding to the aforesaid target air-fuel ratio, when it isjudged that the vehicle is in the steady running condition.

More specifically, for the purpose of improving the fuel comsumption,the target air-fuel ratio leaner than the stoichiometric air-fuel ratiois predetermined in accordance with the engine operating condition,during the predetermined running condition where an engine load iswithin a predetermined range of value and a variation in the engine loadis at a predetermined value or less, the air-fuel ratio is graduallyapproached to the target air-fuel ratio every predetermined period oftime in accordance with the engine operating condition, and the ignitiontiming is gradually approached to the required ignition timingcorresponding to the target air-fuel ratio every predetermined period oftime.

The arrangement according to a second aspect of the present inventioncomprises: fuel injection control means for controlling the on-offtiming a fuel injection valve in accordance with fuel injectionpulse-width (fuel injection time duration) corresponding to the enginerotational speed and engine load; ignition timing control means forcontrolling the on-off timing of an igniter in accordance with the sparkadvance angle corresponding to the engine rotational speed and engineload; memory means for previously storing the target air-fuel ratioleaner than the stoichiometric air-fuel ratio in accordance with theengine operating condition; judging means for judging whether or not theengine load is within the predetermined range of value and the variationin the engine load is at the predetermined value or less, based on adetected result from load detecting means; fuel injection correctingmeans for correcting the on-off timing of the fuel injection valve sothat the air-fuel ratio gradually approaches the target air-fuel ratioobtained through the result of detection from engine operating conditiondetecting means every predetermined period of time, based on the resultof judgement from the judging means; and ignition timing correctingmeans for correcting the on-off timing of the igniter so that theigniton timing gradually approaches the required ignition timingcorresponding to the target air-fuel ratio obtained in such a manner asaforesaid every predetermined period of time, based on the result ofjudgement from the judging means.

The above-described arrangement of the present invention is advantageousin that, during the predetermined vehicle running condition, theair-fuel ratio is gradually controlled to the target air-fuel ratioaiming at improvements in the fuel consumption and the ignition timingis controlled to the required ignition timing corresponding to thisair-fuel ratio, so that the fuel consumption can be improved withouthampering the controllability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of the engine, to whichthe present invention is applied;

FIG. 2 is a block diagram showing the control circuit of FIG. 1;

FIG. 3 is a chart showing an example of the target air-fuel ratio;

FIG. 4 is a chart showing an example of the required ignition timingcorrection value;

FIG. 5 is a flow chart showing the routine of judging the air-fuel ratiocorrection and the ignition timing correction;

FIG. 6 is a flow chart showing the routine of controlling the air-fuelratio and the ignition timing;

FIG. 7 is a flow chart showing another example of the routine of theair-fuel ratio correction and the ignition timing correction; and

FIG. 8 is a chart showing another example of the target air-fuel ratio.

DETAILED DESCRIPTION OF THE INVENTION

Detailed description will hereunder be given of one embodiment of thepresent invention. FIG. 1 is the schematic diagram of the spark-timingengine, to which the present invention is applied. An air flow meter 2is provided downstream of an air cleaner, not shown. This air flow meter2 comprises a compensation plate 2A rotatably provided in a dampingchamber, a measuring plate 2B rotatable in association with thecompensation plate 2A and a potentiometer 2C for converting the rotationof the measuring plate 2B into a voltage. A throttle valve 4 is provideddownstream of the air flow meter 2. This throttle valve 4 is mountedthereto with an idle switch 6 movable in association with the throttlevalve 4 and adapted to be turned on when the throttle valve is fullyclosed, to be turned off when the throttle valve is opened. Disposeddownstream of the throttle valve 4 is a surge tank 8 which iscommunicated with a combustion chamber 12 through an intake manifold 10.This intake manifold 10 is mounted thereto with fuel injection valves 14for respective cylinders. The combustion chamber 12 is communicated witha catalytic converter 18 filled up with a three-way catalyst through anexhaust manifold 16. Furthermore, an engine block is secured theretowith a coolant temperature sensor 20 for detecting coolant temperatureof the engine to output a coolant temperature signal. Projected into thecombustion chamber of the engine is the forward end of a spark plug 22connected to a distributor 24. The distributor 24 is provided thereinwith a cylinder discriminating sensor 26 and an engine speed sensor 28,each of which comprises a pickup fixed to a distributor housing and asignal rotor fixed to a distributor shaft. In a six-cylinder engine forexample, the cylinder discriminating sensor 26 outputs a cylinderdiscriminating signal to a control circuit 30 comprising a microcomputeror the like at every 720°CA (crank angle) for example, and the enginespeed sensor 28 outputs an engine signal to the control circuit at every30°CA. The distributor 24 is connected to an igniter 32. In addition,descignated at 34 is a vehicle speed sensor for detecting the rotationof a transmission output shaft to output a vehicle speed signal.

As shown in FIG. 2, the control circuit 30 includes a central processingunit (CPU) 36, a read only memory (ROM) 38, a random access memory (RAM)40, a backup RAM (BU-RAM) 42, an input/output port (I/O) 44, ananalogue/digital converter (ADC) 46 and buses such as a data bus and acontrol bus, which connect the above-described components to oneanother. Inputted to the I/O 44 are the cylinder discriminating signal,the engine speed signal and an idle signal from the idle switch 6. TheI/O 44 outputs a fuel injection pulse signal for controlling the on-offtiming of the fuel injection valve 14 and an ignition pulse signal forcontrolling the on-off timing of the igniter 32 through drive circuits,not shown, respectively. Furthermore, an intake air flowrate signal fromair flow meter, the vehicle speed signal and the coolant temperaturesignal are inputted to the ADC 46 and converted into digital signals.The ROM 38 previously stores therein a map of the basic spark advanceangles represented by the engine speeds and the intake air flowrates perturn of the engine, a map of the air-fuel ratios represented by theintake air flowrate per turn of the engine and the target air-fuelratios as shown in FIG. 3, a map of the ignition timing correctionvalues represented by the target air-fuel ratios and the requiredignition timing correction values as shown in FIG. 4, a program ofseeking the fuel injection flowrates from the intake air flowrates perturn of the engine and the like.

The map of the air-fuel ratios is determined such that the targetair-fuel ratio indicated by an excess air rate λ is increased with theincrease of the intake air flowrate per turn of the engine. Furthermore,the map of the ignition timing correction values is determined such thatthe correction value is increased with the increase of the targetair-fuel ratio indicated by the excess air rate λ.

Description will hereunder be given of the routines of this embodiment.The following routines will be described by use of the numerical valuesnot affecting this embodiment, however, these numerical values need notnecessarily be limited thereto. FIG. 5 shows a first routine of judgingwhether the air-fuel ratio and the ignition timing should be correctedor not. In Step 51, an intake air flowrate per turn of the engine or aload Q/N and a variation of load ΔQ/N, both of which are sought from anintake air flowrate and an engine speed N, are read out of the RAM andcorrection values for the target air-fuel ratio and the ignition timingare sought from the map of the ROM by the interpolation method. In Steps52 and 53, it is judged whether or not the load Q/N exceeds 0.3 (l/rev.)and is less than 0.7 (l/rev.). When the load Q/N exceeds 0.3 (l/rev.)and is less than 0.7 (l/rev.), i.e., the load is within the range of thepredetermined value, then in Step 54, it is judged whether or not thevariation of load ΔQ/N is less than 0.1 (l/rev.)/30 (msec), that is,less than the predetermined value. When the load Q/N is within the rangeof the predetermined value and the variation of load ΔQ/N is less thanthe predetermined value, it is regarded that the predetermined runningcondition are present, and Step 55, a flag F is set which permits thecorrections of the air-fuel ratio and the ignition timing. On the otherhand, when it is not regarded that the predetermined running conditionare not present, the flag F is reset in Step 56.

FIG. 6 shows the routine of correcting the air-fuel ratio and theignition timing. In Step 61, it is judged whether or not 50 (msec) haselapsed on the basis of the counted value of a counter in a registerportion of the CPU, that is, the predetermined time period has elapsed.When the predetermined time period has not elapsed, the process goesforward to the subsequent routine, and, when the predetermined timeperiod has elapsed, then in Step 62, it is judged whether or not theflag F permitting the corrections in Step 62 is set. When the flag F isreset, then in Step 63, the air-fuel ratio and the ignition timing,which are regarded as normal values, are controlled. More specifically,during the fuel injection time duration sought from the engine speed Nand the load Q/N, the fuel injection valve is opened, and the igniter ison-off operated so that the ignition can be effected by the basic sparkadvance angle sought from the map of the ROM by the interpolationmethod.

On the other hand, when the flag F is set, then in Step 64, it is judgedwhether or not the air-fuel ratio at present is leaner than the targetair-fuel ratio. When richer, then in Step 65, the air-fuel ratio atpresent is decreased 0.1%, i.e., made leaner by a predetermined value,and the routine proceeds to Step 67. Furthermore, when the air-fuelratio at present is leaner than the target air-fuel ratio, then, in Step66, the air-fuel ratio is equalized to the target air-fuel ratio. As theresult, the air-fuel ratio is controlled to approach the target air-fuelratio by 0.1% per 50 (msec). Description will not be given of this byway of an example when the fuel injection pulse-width (fuel injectiontime duration) is controlled to thereby control the air-fuel ratio.Since the fuel injection pulse-width Tp is longer than the fuelinjection pulse-width Tpo corresponding to the target air-fuel ratio atthe initial stage where the predetermined running condition commence, inStep 65 the fuel injection pulse-width Tp is shortened by 0.1%. Untilthe fuel injection pulse-width Tp is equalized to the fuel injectionpulse-width Tpo, the fuel injection pulse-width Tp is shortened by 0.1%per 50 (msec) as described above.

In Step 67, it is judged whether or not the ignition timing at presentis farther advanced than the required ignition timing sought by adding acorrection value to the basic spark advance angle, i.e., the requiredignition timing corresponding to the corrected air-fuel ratio. When theignition timing at present retards behind the required ignition timing,then, in Step 68, the ignition timing at present is advanced by 0.25°CA,i.e., a predetermined value. Furthermore, as the result of this advance,if the ignition timing at present is farther advanced than the requiredignition timing, in Step 69 the ignition timing is equalized in value tothe required ignition timing. As the result, the igniter is on-offcontrolled so that the ignition timing will be advanced by 0.25°CA per50 (msec) until the ignition timing is equalized in value to therequired ignition timing.

FIG. 7 shows a second routine of judging whether or not the correctionsof the air-fuel ratio and the ignition timing should be made.Additionally, same reference numerals as shown in FIG. 5 are used inFIG. 7 to designate same or similar parts, so that detailed descriptionwill be omitted. To detect the predetermined running condition, in thisroutine, there are further judged the vehicle speed, coolant temperatureand the conditions of throttle valve and the controlled conditions ofthe air-fuel ratio. In Step 71, it is judged whether or not the vehiclespeed exceeds 40 (Km/h) based on the vehicle speed signal. In Step 72,it is judged whether or not the engine coolant temperature is within therange of 80° C.-95° C. In Step 73, it is judged whether or not the idleswitch is off, i.e., the throttle valve is opened. In Step 74, it isjudged whether the air-fuel ratio is not controlled so as to be richerthan the stoichiometric air-fuel ratio by the fuel increase effectedduring the high load. When the requirements in connection with the loadas shown in FIG. 5 and the above-described requirements are satisfied,the correction flag F is set. In addition to the above-describedrequirements, it may be judged whether or not a constant speed runningdevice for holding the vehicle speed at a predetermined value is inoperation.

FIG. 8 shows an example of another map of the target air-fuel ratio. Thetarget air-fuel ratio in this map is determined such that the excess airrate λ increased, i.e., the air-fuel ratio becomes leaner, with theincrease of the vehicle speed.

In addition, in the foregoing, there has been explained the examplewhere the air-fuel ratio and the ignition timing are controlled by theintake air flowrate and the engine speed, however, the present inventionis applicable to an engine in which the air-fuel ratio and the ignitiontiming are controlled by the intake pipe pressure and the enginerotational speed. Furthermore, there has been explained the examplewhere the required ignition timing is obtained from the correction valuefor the ignition timing, however, the required ignition timing itselfcan be stored in the form of a map.

What is claimed is:
 1. A method of controlling an air-fuel ratio and anignition timing in an internal combustion engine of a vehicle comprisingthe steps of:(a) controlling an on-off timing of a fuel injection valvein accordance with fuel injection time duration corresponding to theengine rotational speed and the engine load; (b) controlling an on-offtiming of an igniter in accordance with a spark advance anglecorresponding to the engine rotational speed and the engine load; (c)determining whether or not the engine load of the vehicle is within apredetermined range and the variation in the engine load is also withina predetermined range; (d) correcting the air-fuel ratio to a targetair-fuel ratio which is leaner than the stoichiometric air-fuel ratio,when it is determined at the step (c) that the engine load and thevariation thereof are within a predetermined range respectively; (e)correcting the ignition timing to a ignition timing corresponding tosaid target air-fuel ratio when the air-fuel ratio is corrected to saidtarget air-fuel ratio at step (d).
 2. A method of controlling anair-fuel ratio and an ignition timing in an internal combustion engineas set forth in claim 1, wherein the determining step is repeatedly madeat a predetermined period of time such as every 50 msec.
 3. A method ofcontrolling an air-fuel ratio and an ignition timing in an internalcombustion engine as set forth in claim 1, including correcting theair-fuel ratio to said target air-fuel ratio when the vehicle speed isat a predetermined value or more; the engine coolant temperature iswithin a predetermined range; no idling is in operation; and theair-fuel ratio is not controlled so as to be richer than thestoichiometric air-fuel ratio.
 4. A method of controlling an air-fuelratio and an ignition timing in an internal combustion engine as setforth in claim 1, wherein said target air-fuel ratio is determined to beleaner in accordance with the increase of the engine load.
 5. A methodof controlling an air-fuel ratio and an ignition timing in an internalcombustion engine as set forth in claim 1, wherein said target air-fuelratio is determined to be leaner in accordance with the increase of thevehicle speed.
 6. A method of controlling an air-fuel ratio and anignition timing in an internal combustion engine as set forth in claim1, wherein said corrected ignition timing becomes advanced as saidtarget air-fuel ratio becomes leaner.